How to Adjust a Lawn Mower Chain

Lawn mowers with chain-driven transmissions use a chain and sprocket system to move the mower forward and help rotate the blades. Because these drive chains stretch over time, they require periodic adjustments to maintain the appropriate tension. Many mower manufacturers recommend having the drive chain adjusted after the first 10 to 15 hours of use and every 25 to 30 hours of subsequent use. Careful, regular adjustments may extend the life of the chain and sprocket assembly components.

Things You'll Need

Screwdriver

Adjustable wrench

Turn off the motor and allow the mower to cool completely. Disconnect the spark plug wire to prevent the mower from accidentally starting while you're adjusting the drive chain.

Take out the screws securing the drive chain cover; the type and number of screws varies by brand and model. Remove the drive chain cover to reveal the chain and sprocket assembly. Loosen, but do not remove, the bolts on the front of the assembly.

Find the adjustment nut directly behind the sprocket assembly. Turn the adjustment nut clockwise to tighten the chain tension or counterclockwise to loosen it. Adjust the mower chain so that the slack side has no more than a half-inch of give at the midpoint.

Tips & Warnings

Remove the drive chain from the assembly if your mower model doesn't have an adjustment nut. Find the chain's master link and open it with a small, flat-head screwdriver. Remove the master link. Remove or add links as needed to adjust the chain tension.

Many mower manufacturers recommend that drive chain adjustments be completed by authorized technicians. Adjusting the chain yourself may void the warranty on the mower.

Over-tightening the chain causes the sprocket assembly to wear out prematurely.